Argon isotopic zoning in mantle phlogopite
Incremental-heating and laser-probe /sup 40/Ar//sup 39/Ar analyses were performed on phlogopite extracted from a garnet-lherzolite mantle nodule entrained by the Precambrian (1200 Ma) Premier kimberlite, South Africa. The spatial resolution of the laser probe has enabled the characterization of argon isotopic zoning in a single phlogopite grain. An apparent age contour map records lower ages (1.2 Ga) along grain margins and high apparent ages (up to 2.4 Ga) at the core. The latter ages are caused by excess argon contamination and subsequent partial diffusive loss, and have no age significance. Comparison with step-heating results indicates that argon spatial distributions inferred from in-vacuo step-heating experiments are, at best, grossly approximate. Variations in the laser-probe apparent ages were observed only laterally across the phlogopite cleavage surface, indicating that argon transport occurs preferentially along phlogopite cleavage planes. Age profiles, when modeled using one-dimensional radial geometry (cylindrical coordinates), do not conform to classical Fick's law diffusion, suggesting that the characteristic dimension of diffusion for argon in phlogopite may be highly variable within individual grains.
- Research Organization:
- Princeton Univ., NJ (USA)
- OSTI ID:
- 6935770
- Journal Information:
- Geology; (United States), Vol. 16:6
- Country of Publication:
- United States
- Language:
- English
Similar Records
Mantle-derived argon components in phlogopite from southern African kimberlites
Mantle metasomatism
Related Subjects
GEOLOGIC DEPOSITS
AGE ESTIMATION
SOUTH AFRICA
ARGON 39
ARGON 40
DIFFUSION
HEATING
ISOTOPE DATING
ISOTOPE RATIO
LASERS
MEASURING METHODS
VARIATIONS
AFRICA
ARGON ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
ISOTOPES
LIGHT NUCLEI
NUCLEI
RADIOISOTOPES
STABLE ISOTOPES
YEARS LIVING RADIOISOTOPES
580100* - Geology & Hydrology- (-1989)